Portion of a skylight



FIG. 1 is a top-front perspective view of a portion of a skylight showing our new design;

FIG. 2 is a left-front perspective view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a top view thereof; and,

FIG. 5 is a right side view thereof.

The broken lines immediately adjacent to the shaded area represent unclaimed boundaries of the design. The broken lines showing the remainder of the portion of a skylight are for environmental purposes only and form no part of the claimed design. 

The ornamental design for a portion of a skylight, as shown and described 